Contributing to the decarbonization of the glass industry.
The glass industry accounts for approximately 1% of the entire manufacturing industry’s total energy consumption. Melting is a particularly energy-intensive process that burns fossil fuels and heats both the glass and the entire furnace to over 1,000℃.
A furnace capable of processing 100 tons of glass daily is estimated to discharge approximately 13 tons of CO2 every day. Japan’s glass industry produces 6 million tons of glass annually, which equates to approximately 800,000 tons of CO2emissions per year – a tremendous amount by any estimation.
The drive towards carbon neutrality has accelerated the search of methods aimed to decrease CO2 emissions. we have developed a method to apply microwaves to the glass melting process.
Results of Screening Tests
Figure 1 shows the results of heating tests using glass materials A and B, both of which contain multiple components. Microwave irradiation tests were conducted with the upper temperature limit set to 800 °C as a model validation and both glass materials were then heated to the target temperature of 800 °C in less than 10 minutes. The temperature of both glass materials rose rapidly after the test began, requiring 1 minute for material A and 7 minutes for material B. We believe that this rapid heating is the result of the improved microwave absorption capacity of the glass material at each time point.
Significance of Using Microwaves
Conventional processes (Figure 3, top) are generally not energy efficient because they heat the external environment — furnace, air, etc. — along with the glass. Moreover, excessive furnace heating may cause degradation of the product.
Microwaves, on the other hand, utilize an energy transfer method that can directly and selectively heat objects and can therefore be expected to improve energy efficiency. When combined with renewable energy, melting furnace producing 100 tons per day is estimated to produce about 1 ton of CO2emissions per day, a reduction of about 90% compared to conventional processes.
Additionally, the selective heating characteristics of microwaves (Figure 3, bottom) allow melting furnaces to operate at lower temperatures. This should increase melting furnace service life, thereby improving profitability in the glass industry – a sector with significant capital expenditure.
Similar advantages can be found in other high-temperature applications.
Microwaves do not depend on the transmission surface for energy transfer, and there is no theoretical limit to the amount of energy input. Consequently, microwaves can be extended beyond glass melting processes to other high-temperature applications such as calcination.
When microwaves were used in the calcination of metal oxides (Figure 4), we confirmed that the target metal oxide reached approximately 1200 ºC in as little as 20 minutes, similar to the heating test for glass materials (Figure 1). However, the temperature of the insulation material (the external environment) stayed below 200 °C, which suggests that this process also takes advantage of the selective heating properties of microwaves.
Therefore, we believe that microwave process offers a variety of advantages in high-temperature applications, such as energy savings, reduced CO2 emissions, and improved profitability due to the longer service life of treatment facilities.